Between 1979 and 1981 Calatrava worked at the ETH (Eidgenossische Technische Hochschule) and obtained a doctorate on the technology of space frames. After establishing an independent architectural and engineering practice in Zurich in 1981, he rapidly gained an international reputation for his integration of technology and aesthetics, producing dynamic structural forms that challenged traditional practice in both architecture and engineering. Calatrava's most important building designs include the Stadelhofen Railway Station (1983-1990), Zurich, a long, curving, three-level structure that includes a basement underpass and upper-level walkway with connecting bridges. The nature of these spaces is emphasized by the structure: the basement is dominated by heavy, inclined concrete supports, and the upper walkway by the skeletal steel ribs of its cantilevered glazed roof.